<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!
	Color getRandColor(int fc,int bc){//给定范围获得随机颜色
        Random random = new Random();
        if(fc>255) fc=255;
        if(bc>255) bc=255;
        int r=fc+random.nextInt(bc-fc);
        int g=fc+random.nextInt(bc-fc);
        int b=fc+random.nextInt(bc-fc);
        return new Color(r,g,b);
    }
%>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">   
<%
	//设置页面不缓存
	/* response.setHeader("PRagma","no-cache");
	response.setHeader("Cache-Control","no-cache");
	response.setDateHeader("Expires", 0); */
	// 在内存中创建图象
	int width=60, height=20;
	BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
	// 获取图形上下文
	Graphics g = image.getGraphics();
	//生成随机类
	Random random = new Random();
	// 设定背景色
	g.setColor(getRandColor(200,250));
	g.fillRect(0, 0, width, height);
	//设定字体
	g.setFont(new Font("Times New Roman",Font.PLAIN,18));
	//画边框
	//g.setColor(new Color());
	//g.drawRect(0,0,width-1,height-1);
	// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
	g.setColor(getRandColor(160,200));
	for (int i=0;i<155;i++)
	{
	 int x = random.nextInt(width);
	 int y = random.nextInt(height);
	        int xl = random.nextInt(12);
	        int yl = random.nextInt(12);
	 g.drawLine(x,y,x+xl,y+yl);
	}
	// 取随机产生的认证码(4位数字)
	String sRand="";
	for (int i=0;i<4;i++){
	    String rand=String.valueOf(random.nextInt(10));
	    sRand+=rand;
	    // 将认证码显示到图象中
	    g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
	    g.drawString(rand,13*i+6,16);
	}
	// 将认证码存入session
	session.setAttribute("validationCode",sRand);
	// 图象生效
	g.dispose();
	// 输出图象到页面
	ImageIO.write(image, "JPEG", response.getOutputStream());
	out.clear();
	out = pageContext.pushBody();
%>